a. Field of the Invention
The instant invention is directed toward a brush electrode and a method for using the brush electrode for tissue contact and thermal assessment, e.g., during ablation procedures. In particular, the brush electrode of the present invention comprises a plurality of flexible filaments or bristles which may be used for applying ablative energy (e.g., RF energy) to tissue during the formation of spot or continuous linear lesion, and means for tissue contact and thermal assessment during these procedures.
b. Background Art
It is well known that benefits may be gained by forming lesions in tissue if the depth and location of the lesion being formed can be controlled. In particular, it can be desirable to elevate tissue temperature to around 50° C. until lesions are formed via coagulation necrosis, which changes the electrical properties of the tissue. For example, when good or sufficiently deep lesions are formed at specific locations in cardiac tissue via coagulation necrosis, undesirable atrial fibrillations may be lessened or eliminated. The definition of “good” or “sufficiently deep” lesions depends at least to some extend on the procedure and may also depend on other considerations, such as tissue characteristics.
Several difficulties may be encountered, however, when attempting to form these lesions at specific locations using some existing ablation electrodes. For example, when forming lesions with RF energy, high temperature gradients are often encountered in the vicinity of the electrode. These high temperature gradients may result in the formation of undesirable coagulum and charring of the surface tissue. For example, undesirable coagulum may begin to form when blood reaches about 80° C. for an appreciable length of time, and undesirable tissue charring and desiccation may be seen when tissue reaches around 100° C. for an appreciable length of time. There are two types of undesirable coagulum. Coagulum may adhere to and damage the medical device itself. In addition, coagulum blood clots or curds may enter a patient's bloodstream, possibly resulting in other health problems for the patient. Charring of the surface tissue may also have deleterious effects on a patient.
As the temperature of the electrode is increased, the contact time required to form the lesions decreases, but the likelihood of charring surface tissue and forming undesirable coagulum increases. As the temperature of the electrode is decreased, the contact time required to form the lesions increases, but the likelihood of charring surface tissue and forming undesirable coagulum decreases. It is, therefore, a balancing act trying to ensure that tissue temperatures are adequately high for long enough to create good or sufficiently deep lesions, while still preventing or minimizing coagulum formation and/or charring of the surface tissue.
Thus, there remains a need for thermal assessment during ablation procedures.
Another difficulty encountered with existing ablation electrodes is ensuring adequate tissue contact. Maintaining adequate tissue contact for forming continuous linear lesions is not always readily determined using conventional fluoroscopy techniques. Instead, the physician determines tissue contact based on his/her experience maneuvering the electrode during the ablation procedure. Such experience only comes with time, and may be quickly lost if the physician does not use the electrode for ablation procedures on a regular basis. When used inside the heart, the beating heart further complicates matters by making it difficult to assess and maintain sufficient contact with the tissue for a sufficient length of time to form a desired lesion. If the contact between the electrode and the tissue cannot be properly maintained, a quality lesion is unlikely to be formed.
Thus there remains a need for tissue contact assessment during ablation procedures.